import java.io.IOException;
import java.net.DatagramPacket;
import java.net.DatagramSocket;
import java.net.SocketException;

public class UdpEchoServer {
    private DatagramSocket socket = null;

    public UdpEchoServer(int post) throws SocketException {
        socket = new DatagramSocket(post);
    }
    public void start() throws IOException {
        System.out.println("服务器启动!!!");
        //1. 通过"死循环"不断处理客户端的请求
        while(true){
            //1. 读取客户端的请求并解析
            DatagramPacket requestPacket = new DatagramPacket(new byte[4096], 4096);
            socket.receive(requestPacket);
            // 上述收到的数据, 是二进制 byte[] 的形式体现的. 后续代码如果要进行打印之类的处理操作
            // 需要转换为二进制才好处理.
            String request = new String(requestPacket.getData(), 0, requestPacket.getLength());
            //2. 根据请求计算响应
            String response = process(request);
            //3. 把响应写回客户端
            DatagramPacket responsePacket = new DatagramPacket(response.getBytes(), response.getBytes().length,
                    requestPacket.getSocketAddress());
            socket.send(responsePacket);
            //打印日志
            System.out.printf("[%s:%d] req=%s, resp=%s\n", requestPacket.getAddress(), requestPacket.getPort(),
                    request, response);
        }
    }

    private String process(String request) {
        return request;
    }

    public static void main(String[] args) throws IOException {
        UdpEchoServer server = new UdpEchoServer(9090);
        server.start();
    }
}
